1. Field of the Invention
The present invention relates generally to fluid actuated shift bar housing assemblies for change gear transmissions and particularly to fluid actuated shift bar housing assemblies wherein selectively applied fluid pressure is effective to urge all of the shift bars into a neutral axial position, or to urge a selected one of the shift bars into at least one selectable axially displaced position for engaging a selected transmission gear ratio. More particularly, the present invention relates to a fluid actuated shift bar housing assembly, preferably actuated by a compressible fluid such as compressed air or the like, having a pair of shift bars each having an axially neutral position with one having a first axially displaced position wherein the shift bar is axially displaced from the neutral position in a first axial direction and a second axially displaced position wherein the shift bar is axially displaced from the neutral position in a second axial direction and the other shift bar having an axially displaced position whereby the shift bar is axially displaced from the neutral position. The housing associated with the shift bars has an actuating portion comprising five selectably pressurizable chambers for urging said shift bars into any one of the five selectable axial positions thereof.
2. Description of the Prior Art
Shift bar housing assemblies having a plurality of axially moveable shift bars, also known as shift rails and shift rods, each carrying or associated with a shift fork, that are selectively axially moved to engage or disengage a selected transmission gear by axial movement of a clutch member, or of a gear carrying clutch teeth, are well known in the prior art, as may be seen by reference to U.S. Pat. Nos.: 3,105,395; 3,611,823; 4,152,949; 4,194,410; and 4,445,393, all of which are assigned to the assignee of this invention and are incorporated herein by reference.
Fluid actuated shift bar housing assemblies, usually actuated by pressurized hydraulic fluid or pressurized air, and the controls therefor, are also well known in the prior art, as may be seen by reference to U.S. Pat. Nos.: 2,924,111; 2,931,237; 2,932,371; 2,943,502; 2,943,719; 2,974,766; 4,440,037; and 4,445,393, all of which are assigned to the assignee of this invention are incorporated herein by reference.
While the prior art fluidly actuated shift bar housing assemblies are generally satisfactory and are presently widely utilized, usually for remotely controlled and/or automatically controlled change gear transmissions, the prior art assemblies were not totally satisfactory as they were complicated and/or expensive to produce, install and/or service, and/or utilize springs or other means to center the shift rails in a neutral position which means tended to shift the transmission into neutral in the event of a loss of pressurized fluid which might undesirably render the driven device totally unusable. Due to space limitations and standardization and mass production practice, prior art shift bar housing assemblies are limited in their ability to provide large fluid chambers effective when pressurized to move at least one of the shift bars axially with great force. An example of a shift rod housing assembly that, although effective for its particular purpose, is limited in its ability to apply a large fluid pressure force against shift rod 144 is shown as actuator 152 in FIG. 1 of U.S. Pat. No. 4,555,959, assigned to the assignee of this invention and the disclosure of which is incorporated herein by reference.